1. Field of the Invention
The invention relates to a transparent substrate, particularly of glass, which is provided with a metal nitride layer, particularly with the aim of producing glazings having protection against solar radiation.
2. Discussion of the Background
Glazings provided with a metal nitride layer make it possible to reduce the heat resulting from solar radiation, because metal nitride layers, e.g. of titanium nitride, are able to partly filter the same by absorption and reflection.
Different methods exist for depositing metal nitride layers on substrates, such as in particular those using a vacuum of the cathode sputtering type assisted by a magnetic field. Although these methods are effective they are expensive with respect to the equipment required and are unable to operate continuously on a float glass ribbon.
These are also so-called pyrolysis methods, which consist of projecting onto a substrate, raised to a high temperature, nitrogen precursors and metal precursors which, when in contact with one another, decompose on the substrate leaving behind a metal nitride film. These methods are simpler to carry out and in particular can be continuously used on the float glass ribbon.
Thus, EP-B-128,169 discloses a process for the deposition of titanium nitride TiN layers by vapor phase pyrolysis, also known as chemical vapor deposition or CVD, from a titanium precursor, such as titanium tetrachloride, and a nitrogen precursor, in the form of ammonia. However, although the deposition of a single nitride layer gives the substrate sun-shielding properties, it scarcely offers any flexibility with regards to the choice of colors. Moreover, the unprotected nitride layer may oxidize on the production line or subsequently, during a heat treatment on the substrate such as bending, tempering or annealing. Thus, a partly oxidized nitride layer undergoes significant deteriorations of its properties and visual appearance.
It is for this reason that EP-B-239,280 recommends depositing on the nitride layer, a second layer for protecting it and constituted by an oxide of tin, silicon or aluminum. However, the degree of resistance to oxidation obtained in this way by the nitride layer is closely dependent on the intrinsic properties of the protective layer, particularly the choice of the metal forming the oxide, as well as its thickness and these properties will also influence the optical appearance, particularly in reflection, of the carrying substrate.
The object of the invention is therefore to improve upon the protection, particularly against oxidation, of a metal nitride layer deposited on a transparent substrate, without said improvement being detrimental to its optical appearance.